1. Field of the Invention
The present invention relates to an exposure apparatus, a making method of the exposure apparatus, and a device manufacturing method. More particularly, the present invention relates to an exposure apparatus and the method of making the apparatus used in lithographic process, to transfer a pattern formed on a mask onto a substrate when manufacturing devices such as a semiconductor device, a pick up device (such as a CCD), a liquid crystal display device, and a thin-film magnetic head device. The present invention shows a superb effect, when applied to an exposure apparatus using vacuum ultraviolet light as an illumination light for exposure.
2. Description of the Related Art
In the case of manufacturing devices such as semiconductors, as an exposure apparatus to transfer a pattern formed on a reticle as a mask onto each shot area of a wafer being coated with a photoresist, conventionally, a step-and repeat-type (a static exposure type) reduction projection type exposure apparatus (a stepper) was often used. Whereas, in recent years, to cope with the demand of a larger transfer pattern subject to exposure without imposing a heavy burden on the projection optical system, a projection exposure apparatus based on a step-and-scan method, that is, a scanning stepper is gathering attention. The scanning stepper sequentially transfers a reduced image on the reticle, by synchronously scanning the reticle and the wafer in respect to the projection optical system in a state where the pattern formed on the reticle is partially projected on the wafer via the projection optical system as a reduced image. This scanning stepper is an exposure apparatus developed by combining the advantage of a transfer method (the slit-scan method) of an aligner, which transfers the entire pattern formed on the reticle by equal magnification on one scanning exposure, and the advantage of the transfer method of the stepper.
Also, with the projection exposure apparatus in general, higher resolution is required. A method of increasing the resolution is to use an illumination light for exposure, which has a shorter wavelength. With the conventional exposure apparatus, an emission line (g line or i line) in the ultraviolet range emitted by an ultra-high pressure mercury lamp has been used. However, recently, light in the deep ultraviolet light region or the vacuum ultraviolet light region such as the KrF excimer laser beam (wavelength: 248 nm) or the ArF excimer laser beam (wavelength: 193 nm) is being used. In addition, the use of a metal vapor laser beam or a harmonic of a YAG laser beam is being considered.
Meanwhile, in the case of using an ultraviolet light such as an excimer light as the illumination light for exposure, the necessity of circulating nitrogen (N2) gas or a gas with ozone removed (such as air) was pointed out. This was due to the fact that the ultraviolet light is absorbed by ozone, as well as in consideration of the properties of the photoresist. However, simply replacing the entire gas within the chamber where the projection optical system is arranged to gas such as nitrogen gas, may cause nitrogen gas with high concentration to leak out, when a worker opens the door of the chamber during maintenance operation by accident.
In order to improve such inconvenience, details of a projection exposure apparatus is disclosed in Japanese Patent Laid Open No. 09-246140, that uses a laser light source emitting a beam having a wavelength range equal to or shorter than the ultraviolet region; houses the illumination optical system, projection optical system, the reticle stage, and the substrate stage separately in a plurality of independent casings; and has a gas supplying means to at least one of the plurality of casings to supply multiple types of gases in the cases with a switching operation. With this projection exposure apparatus, a low absorptive gas to the illumination light for exposure is supplied in the selected casing when usual exposure is performed, whereas in cases when pilot exposure is performed during maintenance gas such as air, which is safe for the worker, is supplied. This allows prevention of the leakage of nitrogen with high concentration almost without fail, and provided the advantage of simplifying the maintenance operation.
As the degree of integration for semiconductor devices become more and more demanding each year, a requirement for improving the resolution of the exposure apparatus have surfaced. For this reason, the KrF excimer laser beam or the ArF excimer laser beam is no longer sufficient enough as the illumination light for exposure. Therefore, possibilities of using a light with a shorter wavelength such as the F2 laser beam (wavelength: 157 nm) or a vacuum ultraviolet light with a shorter wavelength as the illumination light for exposure are being seriously explored. Thus, it is safely said that the F2 laser exposure apparatus is a prime possibility of the exposure apparatus of the next generation.
With the projection exposure apparatus referred to the disclosure above, however, as a premise, the KrF excimer laser beam or the ArF excimer laser beam is used as the illumination light for exposure. Accordingly, two types out of three gases being nitrogen, ozone-depleted air, and air, are used by switching operation.
Also, with the projection exposure apparatus referred to the disclosure above, nitrogen with a low purity level is exhausted to the external atmosphere.
Meanwhile, in the case of using the F2 laser beam or the vacuum ultraviolet light having a wavelength shorter than the F2 laser beam, vacuum ultraviolet light is absorbed by gases such as oxygen, vapor, and hydrocarbon gas on the optical path. And this makes it difficult to secure the sufficient transmittance to the laser beam. Therefore, a possibility can be considered to remove the gases above from the optical path of the laser beam by replacing it with helium gas.
Helium gas, however, is costly, compared with nitrogen gas, therefore; simply replacing nitrogen with helium gas in the disclosure above only increases the cost of the apparatus. Also, when using the F2 laser beam, the degree of chemical cleanliness of the optical path needs to be maintained at a tighter level compared with the case of using ArF excimer laser beam. So, from this point as well, it is not sufficient enough to employ the disclosure above without any modification.
The present invention has been made in consideration of the inconvenience of the prior art, and has as its first object to provide a new exposure method and an exposure apparatus that exhibits high performance in the aspects of the degree of chemical cleanliness and the transmittance to the illumination light for exposure.
It is the second object of the present invent ion to provide a device manufacturing method that can improve the productivity when producing highly integrated microdevices.
According to the first aspect of the present invention, there is provided an exposure apparatus which performs exposure on a substrate with an illumination light from a light source, the exposure apparatus comprising: at least a first type air conditioning room arranged on an optical path between the light source and the substrate, the first type air conditioning room having a short optical path of the illumination light passing through and a predetermined level of chemical cleanliness degree; at least a second type air conditioning room arranged on the optical path, the second type air conditioning room having a longer optical path of the illumination light passing through and a higher degree of chemical cleanliness compared with the first type air conditioning room; a first air conditioning control unit which supplies a first gas to air condition the first type air conditioning room; and a second air conditioning control unit which supplies a second gas to air condition the second type air conditioning room.
Air conditioning, here, means in general, conditioning the air, that is automatically adjusting the temperature or the humidity of the air inside a room so as to maintain the best condition. However, in this description, xe2x80x9cair conditioningxe2x80x9d means not only to condition the air, but also means to send gas into the room so as to maintain the condition of the room at a desired state, likewise with the air conditioning in general.
With the exposure apparatus in the present invention, in the second type air conditioning room, the gaseous portion in which the illumination light (illumination light flux) passes through is long, and require a high degree of chemical cleanliness. Therefore, air conditioning is to be performed with the illumination light kept from being absorbed as much as possible, as well as with a high degree of chemical cleanliness. Meanwhile, in the first type air conditioning room, the distance that the illumination light passes through is short, and the degree of chemical cleanliness is not so high compared with the second type air conditioning room. Therefore, the amount of illumination light absorbed while passing through the gaseous portion is small, therefore the air conditioning require a degree of chemical cleanliness to only some extent. In short, the performance required for air conditioning differs between the first type air conditioning room and the second type air conditioning room.
Therefore, with the exposure apparatus in the present invention, the first air conditioning control unit supplies the first gas to air condition the first air conditioning control unit; and the second air conditioning control unit supplies the second gas to air condition the second type air conditioning room. This allows the first air conditioning control unit and the second air conditioning control unit to independently control the air flow and the contamination by using gases for air conditioning in accordance to the performance required, thus can perform various ideal controls independently. Accordingly, by arranging the optical system in the first air conditioning control unit and by arranging the mask or substrate which do not like dust in the second air conditioning control unit, the transmittance of the optical system can be kept from deteriorating and dust from adhering. Also, the degree of chemical cleanliness respectively required can be easily achieved.
In this case, the second gas can be an inert gas with high purity level, and the first gas can be an inert gas which purity level is lower than the second gas.
With the exposure apparatus in the present invention, the exposure apparatus can further comprise: a third type air conditioning room which houses the first type air conditioning room and the second type air conditioning room; and a third air conditioning control unit which supplies a third gas to air condition the third type air conditioning room. That is, outside the first type air conditioning room and the second type air conditioning room, the third type air conditioning room can be arranged which houses the first type air conditioning room and the second type air conditioning room. And the third air conditioning control unit which supplies a third gas to air condition the third type air conditioning room is also arranged, thus making up a double-structured air conditioning room.
In this case, the second gas used to air condition the second type air conditioning room can be an inert gas with high purity level, and the first gas used to air condition the first type air conditioning room can be an inert gas which purity level is lower than the second gas, and the third gas can be a gas including the inert gas which purity level is lower than that of the first gas.
With the exposure apparatus in the present invention, the exposure apparatus can comprise a main body of the exposure apparatus, which includes an illumination optical system illuminating the mask with the illumination light, a mask stage which holds the mask, a projection optical system projecting the illumination light outgoing from the mask to the substrate, and a substrate stage which holds the substrate, and the first type air conditioning room is at least one of a first air conditioning room which include an edge surface of an image plane side of the projection optical system, the substrate stage and its driving unit, and a second air conditioning room which include an edge surface of an object surface side of the projection optical system, the mask stage and its driving unit, and the second type air conditioning room is at least one of a third air conditioning room which include the projection optical system and a fourth air conditioning room which include the illumination optical system.
In general, in the third air conditioning room and fourth air conditioning room where the optical system is installed, the gaseous portion where the illumination light flux passes through is long, and the absorption of the illumination light has to be suppressed to an extreme as well as require a chemically clean air conditioning. Whereas, in the first air conditioning room and second air conditioning room where the stage system is installed, the gaseous portion where the illumination light flux passes through is short so the amount of illumination light absorbed is small. Therefore, for example, in the case of measuring the stage position using the interferometer, the degree of chemical cleanliness required is a degree that does not affect the measurement precision. However, with the first air conditioning room and second air conditioning room, in order to prevent dust from depositing on the mask, an air flow needs to be generated to some extent. As can be seen, the performance required for air conditioning differs between the first air conditioning room, second air conditioning room and the third air conditioning room, fourth air conditioning room.
With the present invention, the first air conditioning control unit provides the first gas to at least either the first or second air conditioning room. And the second air conditioning control unit provides the second gas to at least either the third or fourth air conditioning room. This allows the first air conditioning control unit and the second air conditioning control unit to independently control the air flow and the contamination by using gases for air conditioning in accordance to the performance required, thus can perform various ideal controls independently. Accordingly, the transmittance of the optical system can be kept from deteriorating and dust from adhering.
In this case, the second gas can be an inert gas with high purity level, and the first gas can be an inert gas which purity level is lower than the second gas. The second gas is the gas supplied to the space in the optical system of the illumination optical system and of the projection optical system, therefore, an inert gas with a high purity level is required so as to keep the contamination level from deteriorating by air conditioning. Whereas, with the stage portion where the maintenance frequency or substrate mask exchanging frequency is high, usage of chemical filters to remove contamination is required, however, the first gas supplied to the stage portion need only the purity level so that it does not affect the measurement accuracy of the interferometer, and does not need to be higher.
With the exposure apparatus in the present invention, the exposure apparatus can further comprise: a stage control unit which drives at least one of the substrate stage and the mask stage housed in the first type air conditioning room, when the first air conditioning control unit supplies the first gas to air condition the first type air conditioning room and replaces internal gas.
In such a case, when replacing the gas within the first type air conditioning room (either one of the first air conditioning room and the second air conditioning room) where the frequency of maintenance is high, the stage control unit drives either the substrate stage or the mask stage which is the specific stage while replacing the gas, therefore, by driving the stage the gas is more positively dispersed, which allows a higher gas replacement speed.
With the exposure apparatus in the present invention, the second air conditioning control unit can operate by a secondary power supply, the second air conditioning control unit starts to operate by the secondary power supply to stop the internal gas of the second type air conditioning room from flowing out as well as to supply an extremely small amount of the second gas when a main power supply of the exposure apparatus is cut off. In such a case, in the projection optical system and the illumination optical system where the maintenance frequency is originally low and does not have many driving portions, the purged state of the second gas can be maintained at all times. Therefore, when starting up the operation of the apparatus, the frequency of having to create a vacuumed state greatly decreases, and this in turn relieves the apparatus from unnecessary stress, as well as reduce the start up time.
With the exposure apparatus in the present invention, partial air conditioning which uses the second gas can be performed in parallel with total air conditioning which uses the first gas in the second type air conditioning room on exposure.
In this case, the second type air conditioning room can have a path which guides the second gas to a specific area inside the second type air conditioning room.
With the exposure apparatus in the present invention, the first type air conditioning room can have the first air conditioning room and the second air conditioning room, and the second type air conditioning room can have the third air conditioning room and the fourth air conditioning room. In such a case, the optical path of the illumination light from the illumination optical system to the substrate is air conditioned by using the first gas or the second gas. With this arrangement, the transmittance of the optical system can be kept from deteriorating, and dust and small particles can also be kept from adhering onto the optical system without fail.
In this case, the first air conditioning room and the third air conditioning room, the third air conditioning room and the second air conditioning room, and the second air conditioning room and the fourth air conditioning room can be respectively divided by a sheet member. In such a case, the adjacent air conditioning rooms are divided by the sheet member, therefore, gases can be replaced with the atmosphere independently, and the work efficiency during maintenance operation is greatly improved. In this case, from the viewpoint of suppressing the degree of chemical cleanliness from decreasing in each chamber, it is preferable for the sheet member to have gone through a chemically cleaned process.
In this case, the sheet member can be a pressure resistant sheet which surface is at least, chemically processed. In such a case, the adjacent air conditioning rooms are divided by the sheet member which is a pressure resistant sheet which surface is at least chemically processed, therefore, the degree of chemical cleanliness decreasing can be suppressed in each chamber. And, also, when replacing the gas in each chamber, gas can be effectively replaced by creating a vacuumed state in each chamber to exhaust the interior gas, and then supplying the inert gas to each chamber.
Alternatively, the sheet member may comprise metal leaf. In such a case, the sheet member which comprises metal leaf can further effectively suppress the vibration from travelling. The sheet member may also be a sheet member made of soft plastic with metal vaporized.
With the exposure apparatus in the present invention, the main body of the exposure apparatus can movably support the substrate stage as well as support the projection optical system, the main body comprising: a first unit supported by a vibration isolation mechanism; and a second unit independent from the first unit in respect to vibration, the second unit supporting a driving unit of the substrate stage; and the sheet member is deformed in accordance with a relative positional change between the first unit and the second unit. In such a case, the sheet member which divides the adjacent air conditioning rooms is deformed in accordance with a relative positional change between the first unit and the second unit, therefore, the sheet member does not interfere the positional change occurring between the first unit and the second unit so vibration does not travel in between the first unit and the second unit. Accordingly, the vibration of the second unit side which supports the driving unit of the substrate stage can be kept from being the cause of vibration occurring in the first unit side which supports the projection optical system, as well as divide each air conditioning rooms with the sheet members.
In this case, the first unit can also movably support the mask stage; and the second unit can also support a driving unit of the mask stage.
With the exposure apparatus in the present invention, in the case the exposure apparatus comprises the first unit and the second unit, the sheet member can be fastened to each unit by a fastening mechanism, the fastening mechanism fastens the sheet members in a state where the sheet member is clamped between two members which surface roughness is below a predetermined level, and the fastening mechanism can be unfastened. In such a case, the sheet member is fastened to the first unit and the second unit via two members (for example spacers) which surface roughness is below the predetermined level and is arranged on the inner surface and outer surface of the sheet member by a fastening mechanism. By fastening the sheet member and each unit so that they are in close contact, gas contamination can be prevented. And compared with the case when the dividing material is made of a rigid material, downsizing is possible. Also, the fastening mechanism can be easily resolved, therefore, compared with the case when the dividing material is fixed, work efficiency during maintenance operation can be improved.
With the exposure apparatus in the present invention, in the case the exposure apparatus comprises the first air conditioning room and the second air conditioning room as the first type air conditioning room and the third air conditioning room and the fourth air conditioning room as the second type air conditioning room, the second gas used to air condition the third air conditioning room and the fourth air conditioning room can be an inert gas with high purity level, and the first gas used to air condition the first air conditioning room and the second air conditioning room can be an inert gas which purity level is lower than the second gas.
In this case, the inert gas may be nitrogen, neon, argon, krypton, xenon, or it may be helium gas.
With the exposure apparatus in the present invention, in the case the third air conditioning room and the fourth air conditioning room is air conditioned with the inert gas with high purity level (the second gas), and the first air conditioning room and the second air conditioning room is air conditioned with the inert gas which purity level is lower than the second gas (the first gas), the exposure apparatus can comprise: a fifth air conditioning room including the first to fourth air conditioning rooms; and a third air conditioning control unit which air conditions the fifth air conditioning room.
In this case, the exposure apparatus can further comprise: a first concentration sensor which individually detects concentration of the inert gas in a gas respectively used to air condition the first to fourth air conditioning rooms; and a first monitoring unit which monitors the concentration of the inert gas in the gas respectively used to air condition the first to fourth air conditioning rooms in accordance with an output of the first concentration sensor; wherein when the concentration of the inert gas of the gas used to air condition at least one of the first and second air conditioning rooms, which is a first specific air conditioning room, is detected to have fallen below a predetermined concentration by the first monitoring unit, the first air conditioning control unit freshly supplies the first gas to the first specific air conditioning room, while exhausting the gas used to air condition the first specific air conditioning room to the third air conditioning control unit so as to use the gas to air condition the fifth air conditioning room, and when the concentration of the inert gas of the gas used to air condition at least one of the third and fourth air conditioning rooms, which is a second specific air conditioning room, is detected to have fallen below a predetermined concentration by the first monitoring unit, the second air conditioning control unit freshly supplies the second gas to the second specific air conditioning room, while exhausting the gas used to air condition the second specific air conditioning room to the third air conditioning control unit so as to use the gas to air condition the fifth air conditioning room.
In such a case, when the concentration of the inert gas of the gas used to air condition at least one of the first and second air conditioning rooms, which is the first specific air conditioning room, falls below the threshold value, the decline in the concentration is detected by the first monitoring unit in accordance with the output of the first concentration sensor. When the decline is detected, the first air conditioning control unit newly supplies the first gas into the first specific air conditioning room, as well as exhaust the gas used to air condition the first specific air conditioning room to the third air conditioning control unit so that the gas can be used to air condition the fifth air conditioning room. Meanwhile, when the concentration of the inert gas of the gas used to air condition at least one of the third and fourth air conditioning rooms, which is the second specific air conditioning room, falls below the threshold value, the decline in the concentration is detected by the first monitoring unit in accordance with the output of the first concentration sensor. And when the decline is detected, the second air conditioning control unit newly supplies the second gas into the second specific air conditioning room, as well as exhaust the gas used to air condition the second specific air conditioning room to the third air conditioning control unit so that the gas can be used to air condition the fifth air conditioning room. Thus, the third air conditioning control unit uses the exhausted gas to air condition the fifth air conditioning room.
Originally, the gas within the first to fourth air conditioning rooms needs to be replaced with an inert gas with a high purity (the purity level of the inert gas of the first gas supplied to the first and second air conditioning rooms may be lower than the second gas supplied to the third and fourth air conditioning rooms, but requires a purity to some extent) and if the purity level declines it cannot be used as it is. However, as is with the present invention, in the case the gas which purity level has declined is supplied to the fifth air conditioning room (total air conditioning room) that include the first to fourth air conditioning rooms, even if the pressure in the interior of the first to fourth air conditioning rooms is not positive, the gas which may flow into the first to fourth air conditioning rooms by a small amount is the inert gas, therefore, compared with the case of performing total air conditioning with N2 or dry air the speed of the purity of the inert gas in the first to fourth air conditioning rooms deteriorating can be greatly slowed down. That is, the space filled with the inert gas can be formed of a double-structure, and this allows the amount of the inert gas supplied to the air conditioning rooms to be suppressed.
In this case, the first concentration sensor can include at least one of an impurities concentration sensor and an ozone sensor. In such a case, when the measurement value of the first concentration sensor exceeds a predetermined permissive value, it can be detected that the concentration of the inert gas within the gas used to air condition the first to fourth air conditioning rooms has fallen below the predetermined concentration value.
With the exposure apparatus in the present invention, the exposure apparatus can further comprise: a storing mechanism which stores gas used for air conditioning for recycling; a second concentration sensor which detects concentration of the inert gas in gas used to air condition the fifth air conditioning room; and a second monitoring unit which monitors the concentration of the inert gas in the gas used to air condition the fifth air conditioning room; wherein when the second monitoring unit detects that the concentration of the inert gas in the gas has fallen below a predetermined concentration, the third air conditioning control unit can exhaust the gas used to air condition the fifth air conditioning room into the storing mechanism. In such a case, gas which purity level of inert gas declined, used to air condition the first to fourth air conditioning rooms, is sent to the fifth air conditioning room. This gas is used to air condition the fifth air conditioning room, and when the purity level of the gas falls below the predetermined concentration, this decline is detected by the second monitoring unit in accordance with the output of the second concentration sensor. When the decline is detected, then the third air conditioning control unit exhausts the gas used to air condition the fifth air conditioning room to the storing mechanism. As is described, the gas that has been used to air condition the rooms which purity has declined, is not exhausted externally, and is stored in the storing mechanism, therefore, polluting the environment can be avoided, as well as the worker from inhaling the gas. Also, since the gas stored in the storing mechanism is recycled, it leads to cutting the cost.
In this case, the second concentration sensor can include at least one of an impurities concentration sensor and an ozone sensor. In such a case, when the measurement value of the second concentration sensor exceeds a predetermined permissive value, it can be detected that the concentration of the inert gas within the gas used to air condition the fifth air conditioning room has fallen below the predetermined concentration value.
According to the second aspect of the present invention, there is provided an exposure method to perform exposure on a substrate with illumination light from a light source, the exposure method comprising; providing a first gas to a first space which is arranged on an optical path between the light source and the substrate, the space having a short optical path of the illumination light passing through and a predetermined level of chemical cleanliness degree; providing a second gas to a second space which has a longer optical path of the illumination light passing through compared with the first space; and performing exposure on the substrate with the illumination light from the light source after the first space is filled with the first gas and the second space is filled with the second gas.
In this case, the second gas can be an inert gas with high purity level, and the first gas can be an inert gas which purity level is lower than the second gas.
In this case, a third space may house the first space and the second space, and a third gas may be supplied to the third space.
In this case, the third gas can be an inert gas which purity level is lower than that of the first gas.
In this case, a stage which holds the substrate can be housed in the first space, and an optical system to perform exposure on the substrate with the illumination light can be housed in the second space.
Also, by using the exposure apparatus or the exposure method according to the present invention in the lithographic process, the pattern can be accurately formed on the substrate, and as a consequence, can manufacture microdevices having a higher integration with higher yield. Therefore, according to the third aspect of the present invention, there is provided a device manufacturing method, which uses the exposure apparatus or the exposure method of the present invention.